Photosynthesis and Respiration Teacher.doc

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Photosynthesis and Respiration

Objectives ? Explain why cells need energy. ? Summarize how energy is captured and stored. ? Describe how plants and animals get energy.

The BIG Idea ? All cells need energy and materials for life processes.

Key Concept ? Cells capture and release energy.

All cells need energy. ? To stay alive, cells need a constant supply of energy. Animal cells get energy from food, while plant cells get energy from sunlight. All cells use chemical energy. ? Chemical energy is the energy stored in the bonds between atoms of every molecule. To stay alive, cells must be able to release (not create) the chemical energy in the bonds. ? A major source of energy for most cells is stored in a sugar molecule called glucose. When you need energy, cells release chemical energy from glucose. You need food energy to run, walk, and even sleep. Your cells use energy from food to carry out all of their functions. ? Think about muscle cells. When you run, muscle cells release chemical energy from glucose to move your legs. The more you run, the more glucose your muscle cells need. But how do plant cells get more glucose? Plants transform the energy in sunlight into the chemical energy in glucose.

Some cells capture light energy. ? The source of energy for almost all organisms ultimately comes from sunlight. Plants change the energy in sunlight into a form of energy their cells can use--the chemical energy in glucose.

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? All animals benefit from the ability of plants to convert sunlight to food energy. Animals either eat plants, or they eat other animals that have eaten plants.

? Photosynthesis is the process that plant cells use to change the energy from sunlight into chemical energy. Photosynthesis takes place in plant cells that have chloroplasts. Chloroplasts contain chlorophyll, a lightabsorbing pigment, or colored substance, that traps the energy in sunlight.

? The process of photosynthesis involves a series of chemical steps, or reactions. The illustration shows an overview of how photosynthesis changes starting materials into new products. o The starting materials of photosynthesis are carbon dioxide and water. The plant takes in carbon dioxide from the air and water from the soil. o The process takes places when carbon dioxide and water enter the plant's chloroplasts. Then, chlorophyll captures energy from sunlight, which is used to change carbon dioxide and water into new products. o The products of photosynthesis are oxygen and sugars such as glucose. The plant releases most of the oxygen to the air as a waste product and keeps the glucose for its energy needs.

Where is chemical energy stored? In the bonds of molecules What substance is the power source of cells? Glucose What traps energy from sunlight in a plant? Chlorophyll

Summarize photosynthesis in complete sentences. In photosynthesis plants use energy from sunlight to change carbon dioxide and water into glucose and oxygen.

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? There is a chemical equation that represents what happens in photosynthesis:

6H2O + 6CO2 + Light Energy

C6H12O6 + 6O2

? In other words, 6 molecules of water, plus 6 molecules of carbon dioxide and light energy yields 1 molecule of glucose and 6 molecules of oxygen.

? Plants do not immediately use all of the glucose molecules they make. Some of the glucose molecules are linked together to build large carbohydrates called starch.

? Plants can store starch and later break it back down into glucose or other sugars when they need energy. Sugars and starches supply food for animals that eat plants.

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All cells release energy. ? All cells must have energy to function. Glucose and other sugars are cell food--they are the power source for cell activities in almost all living things. ? When glucose is stored as glycogen or taken in as starch, it must be broken down into individual sugar molecules before cells are able to use it. ? Recall that chemical energy is stored in the bonds of sugars. When a sugar molecule is broken down, a usable form of energy is released for the cell's life functions. ? Cells can release energy in two basic processes: cellular respiration and fermentation. Cellular respiration requires oxygen, while fermentation does not. In addition, cellular respiration releases much more usable energy than does fermentation.

Cellular respiration releases energy for the cell. ? In cellular respiration, cells use oxygen to release energy stored in sugars such as glucose. In fact, most of the energy used by the cells in your body is provided by cellular respiration. ? Just as photosynthesis occurs in organelles called chloroplasts, cellular respiration takes place in organelles called mitochondria. Remember that mitochondria are in both plant and animal cells, so both kinds of cells release energy through cellular respiration. ? Like photosynthesis, cellular respiration is a process that changes starting materials into new products. o The starting materials of cellular respiration are sugars--such as glucose--and oxygen. o The process begins when glucose in the cytoplasm is broken down into smaller molecules. This releases a small amount of energy. These molecules then move into the mitochondria. At the same time oxygen enters the cell and travels into the mitochondria. As the smaller molecules are broken down even

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further, hydrogen is released in a way that allows cells to capture energy in a usable form. The hydrogen combines with oxygen to make water. o The products are energy, carbon dioxide, and water. ? Some of the energy released during cellular respiration is transferred to other molecules, which then carry the energy where it is needed for the activities of the cell. The rest of the energy is released as heat. The cell releases the carbon dioxide formed during cellular respiration. ? The image below shows the process of cellular respiration.

? There is a chemical equation that represents what happens in cellular respiration:

C6H12O6 + 6O2

6H2O + 6CO2 + Chemical Energy

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